1. Field of the Invention
The present invention relates to a digital recording and/or reproducing apparatus of a video signal, and more particularly, to a recording apparatus for carrying out bit rate reduction coding of a video signal and digitally recording the coded video signal on a recording medium, a reproducing apparatus capable of digitally reproducing a video signal at a changeable or extraordinary speed from a recording medium having such video signal recorded thereon, and a recording/reproducing apparatus having such digital recording and reproducing functions.
2. Description of the Background Art
In recent years, an apparatus has been developed for recording digitally a video signal on a recording medium and reproducing digitally the same from the recording medium. One such typical apparatus is the so-called digital video cassette recorder (referred to as "digital VCR" hereinafter) which is available for practical use. In such a conventional digital VCR, a digital video signal which is in a bit rate reduction coded (bandwidth compressed) state for the purpose of reducing the enormous amount of information to a level suitable for recording and reproduction is recorded on a magnetic tape and reproduced therefrom using a rotary head.
FIG. 1 is a block diagram schematically showing a structure of the conventional digital VCR using the bit rate reduction coding method. Such conventional digital VCR is disclosed in Japanese Patent Laying-Open No. 2-220270, for example.
Referring to FIG. 1, at the time of recording, a digital video signal provided from a video signal source not shown is supplied to a block shuffling circuit 101 included in a digital VCR. The block shuffling circuit 101 divides the digital video signal into a plurality of blocks, each of which is formed of a plurality of pixels and has a certain size, to rearrange the video signal data on the basis of such blocks.
Then, the digital video signal rearranged by the block shuffling circuit 101 is applied to a bit rate reduction coding circuit 102 where the bit rate reduction coding of data on the basis of each block is carried out to realize an amount of information suitable for recording onto a tape. More specifically, the video signal of each block entered into the bit rate reduction coding circuit 102 is subjected to the well-known orthogonal transform coding, and then subjected to a variable length coding process according to the information amount of each block. As a result, reduction of the data amount, i.e., bit rate reduction coding of the video signal is realized. The video signal is further supplied to an error correction coding circuit 103.
The error correction coding circuit 103 adds an error correction code (parity) to the block data thus subjected to bit rate reduction coding, and supplies the same to a synchronizing signal and ID signal applying circuit 104. The synchronizing signal and ID signal applying circuit 104 adds a synchronizing signal and an ID signal to the supplied video signal to provide the same to a modulation circuit 105.
The modulation circuit 105 modulates the supplied signal while suppressing the direct current (DC) component thereof to record the same on the above-described block basis on a magnetic tape 107 as a recording medium via a magnetic head 106.
At the time of reproduction, recorded data on the tape 107 are reproduced via a magnetic head 108 to be demodulated by a demodulation circuit 109. The demodulated video signal is supplied to a synchronizing signal and ID signal detection circuit 110 where detection of the synchronizing signal and ID signal is carried out. Then, the video signal is applied to an error correction decoding circuit 111.
The error correction decoding circuit 111 carries out error correction of the applied video signal. The corrected data is subjected to variable length decoding and inverse orthogonal transform processes for each block by a decoding and concealment circuit 112 to restore the original data of each block. On the other hand, concealment processing of a video signal is carried out for the portion of data where error correction could not be carried out in the error correction decoding circuit 111.
The data thus subjected to the error correction and decoding process is supplied to a block de-shuffling circuit 113 where the data is rearranged in a manner opposite to that by the block shuffling circuit 101 of the recording system. As a result, the video signal arranged in the original form, i.e., the same form as that at the time of recording is reproduced. The data signal of the block de-shuffling circuit 113 is output appropriately to be provided to a monitor device and the like not shown.
The digital VCR which processes the video signal on the basis of blocks as described above has the following disadvantage, compared with the digital VCR (e.g., D1-format digital VCR) which processes the video signal on the basis of pixels.
In the case where the video signal is processed on the basis of blocks, reproduction at an extraordinary speed such as a high speed search is usually carried out by displaying image data belonging to a plurality of different fields as one reproduced picture on a screen. More specifically, in the case where the processing of a signal is carried out on the basis of pixels and the shuffled pixels are recorded on and reproduced at a high speed from a track, the image data belonging to the plurality of fields are dispersed in the whole picture, so that unnatural discontinuity does not generate in the picture, and thus the picture can has good quality. Meanwhile, in the case where the data are recorded on the basis of blocks including the plurality of pixels and are reproduced at a high speed, blocks belonging to different fields may be adjacent to each other in the reproduced picture and a boundary between such small blocks is visually recognized. If a large number of small blocks belonging to different fields are reproduced in the minutely mixed manner, such boundaries are also generated minutely, resulting in the reproduced picture which appears as if a mosaic pattern processing has been applied. As a result, the quality of the reproduced picture in the high speed reproduction remarkably decreases.